Vehicle speed, as displayed on or by a vehicle speedometer, is based on wheel speed as sensed by wheel speed sensors at each wheel of the vehicle. A control module determines vehicle speed based on the number of revolutions of a wheel, as indicated by the wheel speed sensors, calculated over a predetermined period of time. The accuracy of the vehicle speed is dependent upon the accuracy of the size of the tire associated with the wheel speed sensor. Thus, since the tire size associated with the wheels is known by the manufacturer of the vehicle at the time of assembly of the vehicle, the speed of the vehicle is pre-calibrated based on the known tire size.
If a customer replaces the tires with non-standard tires, such as aggressive off-road tires or snow tires, the speedometer display can be inaccurate if the control module is not updated with the new tire size. It is possible to have the vehicle speed recalibrated upon installation of new tires, as suggested in U.S. Pat. No. 6,313,742. However, such a system requires an affirmative action taken in order to recalibrate the vehicle speed determination including actuation of the calibration system as well as the entering of specific tire data.
Thus, it is an object of the present invention to provide a method and system for automatically calibrating a vehicle speed, as may be displayed on a vehicle speedometer, to accommodate any tire size without requiring a user to initiate the calibration.